Most articles on sites like DailyJS will refer to ECMA-262, ECMAScript 3, and ECMAScript 5. We usually abbreviate these terms to ES3 and ES5.
ECMAScript 5 adds a lot of features that we've already started to take for granted: including new array methods like
Object methods like
Object.create, property attributes, function binding, and more.
Proposals for the language are collected on the strawman wiki, and discussed in detail by several contributors on the wiki and mailing lists. To keep up with this, I often check the wiki's recent changes and the es-discuss mailing list.
The language will change, and as new standards are made available you'll need to know what your given platform or browser supports.